development of a pid controller for dc …umpir.ump.edu.my/456/1/mohd_aizuddin_abu_bakar.pdf ·...

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DEVELOPMENT OF A PID CONTROLLER FOR DC MOTOR USING

MICROSOFT VISUAL BASIC

MOHD AIZUDDIN BIN ABU BAKAR

A report submitted in partial fulfillment of the

requirements for the award of the degree of

Bachelor of Electrical (Electronics) Engineering

Faculty of Electrical and Electronics Engineering

Universiti Malaysia Pahang

NOVEMBER 2008

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4

“I hereby acknowledge that the scope and quality of this thesis is qualified for the award of

the Bachelor Degree of Electrical Engineering (Electronics)”

Signature : ______________________

Name : HASZURAIDAH BINTI ISHAK

Date : 17 NOVEMBER 2008

DEVELOPMENT OF A PID CONTROLLER FOR DC MOTOR USING

MICROSOFT VISUAL BASIC

5

MOHD AIZUDDIN BIN ABU BAKAR

A report submitted in partial fulfillment of the

requirements for the award of the degree of

Bachelor of Electrical (Electronics) Engineering

Faculty of Electrical and Electronics Engineering

Universiti Malaysia Pahang

NOVEMBER 2008

I declare this thesis entitled Develop a PID controller for DC motor using Microsoft

Visual Basic is the result of my own research except as cited in the references. This

thesis has not been accepted for any degree and is not concurrently submitted in

candidature of any other degree

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Signature: _________________________________

Name: MOHD AIZUDDIN BIN ABU BAKAR

Date: 17 NOVEMBER 2008

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ACKNOLEDGEMENT

I am greatly indebted to my supervisor, Puan Haszuraidah binti Ishak for her

advice and guidance throughout my project. Thank you.

I would like to thank my family member for giving me their loves and supports

throughout my study in Universiti Malaysia Pahang.

Special thanks to FKEE staffs for helping me to complete my project.

Suggestions and criticisms from my friends have always been helpful in finding

solutions to my problems. Thank you all.

Finally, I would like to express my thanks to those who involves directly or

indirectly in completion of my project.

ABSTRACT

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This main of this project is to develop a PID (Proportional, Integral, Derivatives)

controller and interface with a device. The controller is PID and the software is

Microsoft Visual Basic 6.0. The MATLAB software is used for simulation of this

system. The methodology is divided into two parts which is software and hardware. The

first part is simulation for this system by using Matlab software to determine the value

of Kp, Ki and Kd. The range value for PID is determined by using Ziegler Nichols

method. For second part is to interface the controller with hardware. The controller is

using Microsoft visual basic 6.0 software. Then, the controller need to interface with

DAQ card first. After interfacing success, the system can be implementing to servo

motor. The feedback value can be received from servo motor encoder. After finished the

first and second part, this system can be tuned up by using the PID value from

simulation.

ABSTRAK

Tujuan utama projek ini adalah untuk membangunkan sebuah pengawal PID

(Proportional, Integral, Derivatives) yang boleh berantaramuka dengan peralatan.

Pengawal yang digunakan adalah PID dan perisian yang digunakan adalah Microsoft

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Visual Basic 6.0. Perisian Matlab digunakan untuk membuat simulasi pada sistem ini.

Metodologi dibahagikan kepada dua bahagian iaitu perkakasan dan perisian. Bahagian

pertama adalah simulasi kepada sistem ini dengan menggunakan perisian Matlab untuk

menentukan nilai Kp, Kid an Kd. Julat nilai PID ditentukan dengan menggunakan

kaedah Ziegler Nicholes. Bahagian kedua adalah untuk antaramuka dantara pengawal

dan perkakasan.Pengawal menggunakan perisian Microsoft Visual Basic 6.0.

Kemudian, pengawal perlu berantaramuka dengan kad DAQ (Data Acquisition).

Selepas berjaya berantaramuka, sistem ini akan diimplementasikan pada motor servo.

Nilai suapbalik akan diterima dari pengekod motor servo. Setelah selesai bahagian

pertama dan kedua, sistem ini akan dilaraskan dengan menggunakan nilai PID dari

proses simulasi.

TABLE OF CONTENTS

CHAPTER TITLE PAGE

10

1

2

3

INTRODUCTION

1.1 Overview

1.2 Project Objectives

1.3 Scope of Project

1.4 Problem Statement

1.5 Thesis Organization

LITERATURE REVIEW

2.1 PID controller

2.2 Direct Current motor

2.3 Microsoft Visual Basic 6.0

2.4 Data acquisition card

METHODOLGY

3.1 Introduction

3.2 Hardware development

3.2.1. Servo motor

3.2.2. Modelling DC servo motor

3.2.3. DAQ card

3.3 Software Development

3.3.1. Matlab

3.3.2. Microsoft Visual Basic 6.0

3.3.3. PID Method

1

1

2

2

3

3

4

4

7

8

9

11

11

14

16

17

20

21

21

21

23

11

4

5

RESULT & DISCUSSION

4.1 No controller

4.2 Proportional controller

4.3 Proportional Integral controller

4.4 Proportional Derivative controller

4.5 Proportional Integral Derivative controller

4.6 Developing PID controller using Microsoft Visual Basic

6.0

CONCLUSION AND RECOMMENDATION

5.1 Conclusion

5.2 Future Recommendation

5.3 Commercialization

5.4 List and Cost of the Component

REFERENCES

APPENDICES A-C

30

31

34

38

41

45

52

53

53

54

54

55

56-88

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LIST OF FIGURES

FIGURE NO.

TITLE PAGE

2.1

2.2

2.3

3.1

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

3.10

3.11

3.12

3.13

4.1

4.2

4.3

4.4

4.5

4.6

4.7

PID controller equations

VB project selection panel

VB development environments

Flow chart of the project

Block diagram of PID controller

Ziegler Nicholes table

Ziegler Nicholes range value

Servo motor

USB DAQ card

System before using PID controller

System with PID controller

Designed using m-file

Typing program

Changing the value

Closed loop system

Save and run

No controller Step input for the system

Proportional controller Kp=70 Output graph for the system

Proportional controller Kp=235

Proportional controller Kp=390

Proportional controller Kp=586

Proportional controller Kp=700

Proportional-integral controller Kp=70 Ki= 0.518

6

8

9

12

13

14

15

16

20

23

24

26

26

27

28

28

31

34

35

35

36

36

38

13

4.8

4.9

4.10

4.11

4.12

4.13

41.4

4.15

4.16

4.17

4.18

4.19

4.20

4.21

4.22

4.23

Proportional-integral controller Kp=700 Ki= 0.518

Proportional-integral controller Kp=70 Ki= 51.8

Proportional-integral controller Kp=700 Ki= 51.8

Proportional-derivative controller Kp=140 Kd= 2.59

Proportional-derivative controller Kp=700 Kd= 2.59

Proportional-derivative controller Kp=140 Kd= 51.8

Proportional-derivative controller Kp=700 Kd= 51.8

PID controller Kp=70 Ki=5.18 Kd=2.59

PID controller Kp=700 Ki=5.18 Kd=2.59

PID controller Kp=70 Ki=518 Kd=51.8

PID controller Kp=700 Ki=518 Kd=51.8

PID controller Kp=70 Ki=5.18 Kd=51.8

PID controller Kp=700 Ki=5.18 Kd=51.8

PID controller Kp=70 Ki=518 Kd=2.59

PID controller Kp=700 Ki=518 Kd=2.59

PID controller using Microsoft Visual Basic 6.0

39

39

40

42

42

43

43

45

46

46

47

48

48

49

50

52

14

LIST OF EQUATIONS

FIGURE NO.

3.1

3.2

3.3

3.4

3.5

3.6

3.7

4.1

4.2

4.3

PAGE

17

17

17

18

18

18

19

31

32

32

15

LIST OF TABLE

TABLE

TITLE PAGE

4.1

4.2

4.3

4.4

4.5

No controller

Comparison of Proportional controller

Comparison of Proportional-integral controller

Comparison of Proportional-derivative controller

Comparison of PID controller

32

37

40

44

50

16

LIST OF APPENDICES

APPENDIX

TITLE PAGE

A

B

C

DAQ card manual

Servo motor manual installation

Microsoft Visual Basic programmed

30

52

61

17

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CHAPTER 1

INTRODUCTION

1.1 Overview

In 18th century, James Watt invented the flyball speed governer to control the

speed of steam engines. In this device, two spinning fliballs rise as rotational speed

increases. A steam valve connected to the flyball mechanism closes with the ascending

flyballs and opens with the descending flyballs, thus regulating the speed.

PID Control (proportional-integral-derivative) is by far the widest type of

automatic control used in industry nowadays. Even though it has a relatively simple

algorithm/structure, there are many subtle variations in how it is applied in industry. PID

control action allows the process control to accurately maintain set point by adjusting

the control outputs.

In order to eliminate this problem, PID controller is introduce to the system.

There‟s few type of controller but in this project, PID controller is chosen to interfaces

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with the DC motor. This is because PID controller helps get the output, where we want

it in a short time, with minimal overshoot and little error.

1.2 Project Objectives

At the end of this project:-

i. To develop a PID controller design for DC motor speed using Microsoft

visual basic.

ii. To control the speed of DC motor with PID controller using Microsoft

Visual Basic (Design the PID controller and tune it).

1.3 Scope of Project

The scope of this project is:-

i. To derive mathematical model of dc motor and develop PID controller

for the motor.

ii. To develop GUI in Vb as an environment to applied the PID controller

for the motor.

iii. Perform computer simulation of the PID controller by using Matlab

simulink to investigate the effectiveness of PID controller.

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1.4 Problem Statements

The speed controller works by varying the average voltage sent to the motor. It

could do this by simply adjusting the voltage sent to the motor, but this is quite

inefficient to do.

A better way is to switch the motor's supply on and off very quickly. However, if the

switching is fast enough, the motor doesn't notice it, it only notices the average effect.

By using PID controller, it can overcome this problems because it is sensitive to

disturbances and able to correct this error quickly.

1.5 Thesis Organization

This thesis will consist of five chapters including this chapter. The contents of

each chapter are outlined as follows;

Chapter 2 will present the detailed description of the PID system, Microsoft

Visual Basic software, DC motor and DAQ card. Chapter 3 will describe the

methodology used in the project, including how the project is organized and flow of the

project. Chapter 4 will discuss about the results and all of this will be concluded in

Chapter 5.

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CHAPTER 2

LITERATURE REVIEW

2.1 PID controller

The PID controller (Proportional, Integral and Derivative) has been known for

several decades in many fields of automatic control. It has had powerful applications

and several modifications anywhere where automatic control has been applicable. In

spite of its many modified structures and forms the basic idea has remained the same.

The underlying working principle relies on feedback control and the PID controller is

the most common embodiment of feedback control. It involves three different terms,

each of which have a specific purpose. Proportional and integral terms were known in

the 1930s but derivative control was not invented until the 1940s. In basic terms, the

PID controller is a numerical recipe, an algorithm. The algorithm may be implemented,

that is, programmed using any programming language supporting numerical

computation. It can be written in Visual Basic, Fortran, Pascal, C or Java. Also, there are

numerous platforms for the algorithm such as personal computers, distributed control

systems (DCS), programmable logic controllers (PLC), and field devices or microchips

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enabling embedded solutions. In spite of the PID controller syntax language and its

platform or even application, there are some essential features that should be involved in

the PID controller algorithm: The basic calculation covering arithmetic around three

different terms is not enough. Other issues of automatic feedback control must also be

taken care of. In addition to this, there are potential characteristics that may be added to

increase functionality and to improve applicability of the PID controller. There are

different types of PID controllers such as ratio, cascade or split range controllers -and

there are different algorithm types such as position or incremental (velocity) algorithms.

The position algorithms can be categorized into ISA, series and parallel algorithms. The

most typical operation modes for PID controllers are automatic, manual, cascade and

remote. Some manufacturers hide their algorithms, but they should be available so that

users can properly tune the instrument. The PID controller is not a secret and it should

not he treated as one, although it is very rare for the numerical robustness of the

algorithm to be available at all.[1]

A proportional–integral–derivative controller (PID controller) is a generic control

loop feedback mechanism widely used in industrial control systems. A PID controller

attempts to correct the error between a measured process variable and a desired set point

by calculating and then outputting a corrective action that can adjust the process

accordingly.[2]

Figure 2.1 shows the PID controller calculation (algorithm) involves three separate

parameters; the Proportional, the Integral and Derivative values. The Proportional value

determines the reaction to the current error, the Integral determines the reaction based

on the sum of recent errors and the Derivative determines the reaction to the rate at

which the error has been changing. The weighted sum of these three actions is used to

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adjust the process via a control element such as the position of a control valve or the

power supply of a heating element.

By tuning the three constants in the PID controller algorithm the PID can provide

control action designed for specific process requirements. The response of the controller

can be described in terms of the responsiveness of the controller to an error, the degree

to which the controller overshoots the set point and the degree of system oscillation.

Note that the use of the PID algorithm for control does not guarantee optimal control of

the system.

Some applications may require using only one or two modes to provide the appropriate

system control. This is achieved by setting the gain of undesired control outputs to zero.

A PID controller will be called a PI, PD, P or I controller in the absence of the

respective control actions. PI controllers are particularly common, since derivative

action is very sensitive to measurement noise, and the absence of an integral value

prevents the system from reaching its target value due to the control action.

Figure 2.1 PID controller equations

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2.2 Direct current motor

Almost every mechanical movement is caused by a DC (direct current) electric

motor. An electric motor is a device that transforms electrical energy into mechanical

energy by using the motor effect.

Every DC motor has six basic parts which is axle, rotor (armature), stator,

commutator, field magnet, and brushes. In most common DC motors, the external

magnetic field is produced by high-strength permanent magnets. The stator is the

stationary part of the motor which includes the motor casing, as well as two or more

permanent magnet pole pieces. The rotor rotates with respect to the stator. The rotor

consists of windings and the windings being electrically connected

to the commutator .Industrial applications use dc motors because the speed-torque

relationship can be varied to almost any useful form which is for both dc motor and

regeneration applications in either direction of rotation. Dc motors are often applied

where they momentarily deliver three or more times their rated torque. In emergency

situations, dc motors can supply over five times rated torque without stalling. Dc motors

feature a speed, which can be controlled smoothly down to zero, immediately followed

by acceleration in the opposite direction. Dc motors respond quickly to changes in

control signals due to the dc motor's high ratio of torque to inertia.[3]

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2.3 Microsoft Visual Basic (VB)

VB is a very easy yet very powerful application development tool under the

Microsoft Windows family. It is possible to get your first program running in less than

an hour. There are three editions of VB, they are the learning edition, the professional

edition, and the enterprise edition. To develop software for control, a professional

edition is necessary.[4]

By using this software as a tuner, it is easier to interface using RS232 port and USB

port. It also can show the input and output data graphically.

Figure 2.2 VB project selection panel

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Figure 2.3 VB development environments

2.4 Data acquisition card

DAQ is an abbreviation for data acquisition. Therefore a DAQ card is a basic A/D

converter coupled with an interface that allows a personal computer to control the

actions of the A/D, as well as to capture the digital output information from the

converter. A DAQ card is designed to plug directly into a personal computer's bus. All

the power required for the A/D converter and associated interface components is

obtained directly from the PC bus.

27

A DAQ card today is more than a simple A/D function on a board. A data acquisition

card can offer measurements of up to 64 channels at a resolution of 16 bits, (one part in

65,536) with data throughput rates up to 20 million samples per second. A data

acquisition card can often include discrete digital bi-directional I/O lines, counter timers,

and D/A converters for outputting analog signals for control applications.

A high-performance DAQ card will work in a very wide range of test and measurement,

and control applications. Combined with powerful software, DAQ cards will turn a

personal computer into powerful measurement system that may be used to automate

experiments, construct product test stands, monitor and control production equipment or

be embedded in products ranging from medical monitoring systems to automobile test

simulators.

A DAQ card converts analog signals into a digital output form, which can be

manipulated with software. Using software in conjunction with a personal computer,

analog data can be displayed, logged, charted, graphed, or stored in memory as needed.

Stored data can later be used and compared with a set of established limits. Control

decisions are made if the stored data is at the limit, above or below the limit. A DAQ

card can make repetitive measurements, for continuous monitoring and controlling.[5]

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CHAPTER 3

METHODOLOGY

3.1 Introduction

This chapter will explain the methodology used in this project. The methodology

is divided into two parts which is hardware and software. The first part is simulation for

this system by using Matlab software to determine the value of Kp, Ki and Kd. The

range value for PID is determined by using Ziegler Nicholes method.

The second part is to interface the controller with hardware. The controller is using

Microsoft visual basic 6.0 software. Then, the controller need to interface with DAQ

card first. After interfacing success, the system can be implementing to servo motor.

The feedback value can be received from servo motor encoder.

Figure 3.1 shows the flow chart of the project. After finished the first and second part,

this system can be tuned up by using the PID value from simulation.

29

Figure 3.1 Flow chart of the project

Find motor transfer function

Simulation in Matlab

Find PID value using Ziegler Nicholes

Develop Visual Basic

Interface with DAQ card

Implement PID onto VB

Interface with servo motor

Finish

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The DAQ card is used as an interface within Visual Basic software and servo

motor. It has analog input, digital input, analog output and digital output port. For this

system, only analog input and output port is used. Servo motor is used to show the

output from controller. It also has a decoder which is used to give a feedback voltage to

the controller. This servo motor input voltage is 5V to 80V.

feedback

Figure 3.2 Block diagram of PID controller

Figure 3.2 shows the block diagram of PID controller. The controller software is

Microsoft Visual Basic 6.0. The PID system is implement in this software where user

can tune the value of Kp, Ki and Kd manually. The value of feedback voltage and error

value shows in this software.

DAQ card

Visual

Basic

Servo

motor

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3.2 Hardware Development

Before starting develop the hardware, the value of P,PI,PD and PID need to

determine first. It is determine using Ziegler Nicholes method. This value is very

important because it will be used as a reference value to tune dc motor using visual

basic software. Figure 3.3 shows Ziegler Nicholes table;

Controller Kp Ki Kd

PID Kpt [0.1 0.5]

Kp max

Kit [0.1 10]

Kp max Tosc

Kdt [0.05 1]

Kp max Tosc

PD Kpt [0.1 0.5]

Kp max

0 Kdt [0.05 1]

Kp max Tosc

PI Kpt [0.1 0.5]

Kp max

Kit [0.01 1]

Kp max Tosc

0

P Kpt [0.05 0.5]

Kp max

0 0

Tosc value: 0.037s

Kp max value: 1400

Figure 3.3 Ziegler Nicholes table

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The Tosc and Kp max value is fixed for this dc motor model [6]. Figure 3.4 shows the

result of Ziegler Nicholes range value;

Controller Kp Ki Kd

PID 140 - 700 5.18 - 518 2.59 – 51.8

PD 140 - 700 0 2.59 – 51.8

PI 140 - 700 0.518 – 51.8 0

P 70 - 700 0 0

Figure 3.4 Ziegler Nicholes range value

The hardware is used after the PID value determined. The hardware used is dc

motor and daq card.

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3.2.1 Servo motor

This dc motor is very suitable for my project. It has encoder to give feedback for

actual speed of the motor. The specification of this dc motor is very suitable for this

project.

Model: CLIFTON PRECISION SERVO MOTOR MODEL JDH-2250-HF-2C-E

Supplier: Servo Systems Company

Specification:

Torque Constant: 15.76 oz-in. / A

Back EMF: 11.65 VDC / KRPM

Peak Torque: 125 oz-in.

Cont. Torque: 16.5 oz-in.

Encoder: 250 counts / rev.

Channels A, B in quadrature, 5 VDC input (no index)

Body Dimensions: 2.25" dia. x 4.35" L (includes encoder)

Shaft Dimensions: 8 mm x 1.0" L w/flat

Figure 3.5 Servo motor

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3.2.2 Modeling DC Servo Motor

The first step of this project is modeling the DC servo motor. Motor modeling is

required in order to obtain the transfer function of the motor which is providing the open

loop system of this project. Then PID controller is adding to changing the system to

closed loop system. Below is the step of the motor modeling.

R= 2.7 Ω

L= 0.004 H

K=0.105 Vs rad-1

K= 0.105 Nm A-1

J= 0.0001 Kg m2

B= 0.0000093 Nms rad-1

araa V

LL

Ki

L

R

dt

di 1 (3.1)

rar

J

Bi

J

K

dt

d

(3.2)

a

r

a

r

a

VLi

J

B

J

K

L

K

L

R

dt

d

dt

di

0

1

(3.3)

35

a

r

aV

iy 010

(3.4)

a

r

a

r

a

Vi

dt

d

dt

di

0

004.0

1

0001.0

0000093.0

0001.0

105.0

004.0

105.0

004.0

7.2

093.01050

25.26675A

0

250B

10C 0D

093.01050

25.26675

0

0

s

sAsI

093.01050

25.26675

s

s

From )(

)(1

AsIdef

AsIadjAsI

(3.5)

If

ac

bd

bcadA

dc

baA

11; (3.6)

ad-bc = (s-675)(s+0.093)-(26.25)(1050)

= s2 + 0.093s – 675s + 62.775 + 27562.5

= s2 + 675.093s + 27625.275

36

6751050

25.26093.0

27625.275 675.093s s

12

1

s

sAsI

27625.275 675.093s s

6751050

25.26093.0

2

s

s

(3.7)

27625.275 675.093s s

262500

)(

)()(

2

sU

sYsT

27625.275 675.093s s

262500

00

250

27625.275 675.093s s

6751050

25.26093.0

10

)(

)()(

2

2

1

s

s

DBAsICsU

sYsT

37

3.2.3 DAQ card

This is the best DAQ card that can support Microsoft Visual Basic software. This

DAQ card use USB port to interface within pc and dc motor. The specification is;

Model: USB 4716

Supplier: Advantech Co. Ltd.

Main Features:

Supports USB 2.0

Portable

Bus-powered

16 analog input channels

16-bit resolution AI

Sampling rate up to 200 kS/s

8DI/8DO, 2 AO and 1 32-bit counter

Wiring terminal on modules

Suitable for DIN-rail mounting

Lockable USB cable for rigid connection

Figure 3.6 USB DAQ card

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3.3 Software Development

3.3.1 Matlab

Before run the VB programming, a simulation of controller using Ziegler Nicholes

value and Matlab software. With this simulation, we can determine the best value for

Kp, Ki and Kd.

3.3.2 Microsoft Visual Basic 6.0

There are many methods to implement into PID controller such as speed, angular

and acceleration. This controller only measure speed (RPM) by using Microsoft Visual

Basic 6.0 edition as a tuner.

Microsoft Visual Basic 6.0 is an object-oriented computer language that can be viewed

as an evolution of Microsoft's Visual Basic (VB) implemented on the Microsoft .NET

framework. Its introduction has been controversial, as significant changes were made

that broke backward compatibility with older versions and caused a rift within the

developer community.

VB Advantage is a powerful VB development productivity utility that enhances VB's

design time environment. VB Advantage has many powerful, helpful, and easy-to-use

features and tools that were conceived to support software engineering development

activities that developers do as they create and test application code.

Like the BASIC programming language, Visual Basic was designed to be easy to learn

and use. The language not only allows programmers to create simple GUI applications,

but can also develop complex applications. Programming in VB is a combination of

visually arranging components or controls on a form, specifying attributes and actions of

those components, and writing additional lines of code for more functionality. Since

default attributes and actions are defined for the components, a simple program can be

39

created without the programmer having to write many lines of code. Performance

problems were experienced by earlier versions, but with faster computers and native

code compilation this has become less of an issue.

Although programs can be compiled into native code executables from version 5

onwards, they still require the presence of runtime libraries of approximately 2 MB in

size. This runtime is included by default in Windows 2000 and later, but for earlier

versions of Windows or Windows Vista, it must be distributed together with the

executable.

Forms are created using drag-and-drop techniques. A tool is used to place controls on

the form. Controls have attributes and event handlers associated with them. Default

values are provided when the control is created, but may be changed by the

programmer. Many attribute values can be modified during run time based on user

actions or changes in the environment, providing a dynamic application. For example,

code can be inserted into the form resize event handler to reposition a control so that it

remains centered on the form, expands to fill up the form. By inserting code into the

event handler for a keypress in a text box, the program can automatically translate the

case of the text being entered, or even prevent certain characters from being inserted.

Visual Basic can create executables (EXE files), ActiveX controls, DLL files, but is

primarily used to develop Windows applications and to interface web database systems.

Dialog boxes with less functionality can be used to provide pop-up capabilities.

Controls provide the basic functionality of the application, while programmers can

insert additional logic within the appropriate event handlers. For example, a drop-down

combination box will automatically display its list and allow the user to select any

element. An event handler is called when an item is selected, which can then execute

additional code created by the programmer to perform some action based on which

element was selected, such as populating a related list.

Alternatively, a Visual Basic component can have no user interface, and instead provide

ActiveX objects to other programs using Component Object Model (COM). This allows

for server-side processing or an add-in module.

The language is garbage collected using reference counting, has a large library of utility

objects, and has basic object oriented support. Since the more common components are

included in the default project template, the programmer seldom needs to specify

additional libraries. Unlike many other programming languages, Visual Basic is

generally not case sensitive, although it will transform keywords into a standard case

configuration and force the case of variable names to conform to the case of the entry

within the symbol table entry. String comparisons are case sensitive by default, but can

be made case insensitive if so desired.

The Visual Basic compiler is shared with other Visual Studio languages (C, C++), but

restrictions in the IDE do not allow the creation of some targets (Windows model

DLL's) and threading models.

40

3.3.3 PID Method

From the modeling DC servo motor, the transfer function is

27625.275 675.093s s

262500

)(

)()(

2

sU

sYsT (3.8)

The system before using PID controller is looks like in Figure 3.7:

Figure 3.7 System before using PID controller

Then, PID controller is added to the system. Now, the system looks like in Figure 3.8:

27625.275 675.093s s

2625002

R Y

41

Figure 3.8 System with PID controller

In Figure 3.8, the variable (e) represents the tracking error which is the

difference between the desired input value (R) and the actual output (Y). This error

signal (e) will be sent to the PID controller, and the controller computes both the

derivative and the integral of this error signal. The signal (u) just past the controller is

now equal to the proportional gain (Kp) times the magnitude of the error plus the

integral gain (Ki) times the integral of the error plus the derivative gain (Kd) times the

derivative of the error (equation 3).

The transfer function of the PID controller is:

s

KsKsKsK

s

KK

ipd

di

p

2

(3.9)

PID controller 27625.275 675.093s s

2625002

R Y

e u

42

So, the signal (u) that is past the controller is:

dt

deKdedtKeKU ip (3.10)

This signal (u) will be sent to the plant, and the new output (Y) will be obtained.

This new output (Y) will be sent back to the sensor again to find the new error signal

(e). The controller takes this new error signal and computes its derivative and its integral

again. This process goes on and on.

In this project, the PID controller that was added into the system is designed

using m-file in matlab software. (Refer Figure 3.9)

Figure 3.9 Designed using m-file

43

Then the following commands are typing into m-file. (Refer Figure 3.10)

Figure 3.10 Typing program

In Figure 3.10, „[num,den] = ss2tf(A,B,C,D‟) command creates the numerator

and denominator of the transfer function of DC servo motor. This numerical

inconsistency can be eliminated by adding the following „num=num(3)‟ command after

the ss2tf command to get rid of the numbers that are not supposed to be there.

The transfer function of PID controller is recalled using following commands.

The value of the proportional gain, Kp, integral gain Ki and derivative gain, Kd can be

adjust by changing the value. (Refer Figure 3.11):